The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in the present disclosure and are not admitted to be prior art by inclusion in this section.
As portable computing devices such as smart phones and tablet computers become more ubiquitous, volatile memory (e.g., dynamic random access memory, or “DRAM”) may be designed to store more and more data in smaller spaces. Memory cells may be reduced in size, and more memory cells may be packed closely together in smaller spaces. These changes may lead to an increase in memory errors.
As volatile memory technologies such as DRAM technologies are scaled to smaller dimensions, reliability issues arise that require mitigation by careful design. One such issue is the noise injected into neighboring cells when a row is activated and refreshed. The voltage swings and current driven when a row (called the aggressor) is activated or refreshed can inject noise into neighboring cells (victims), potentially draining a little bit of charge from the victim's storage capacitors. The more often the aggressor row is activated before its victim neighbors are activated or refreshed, and the weaker the victim cells (smaller charge, higher leakage, etc.), the higher the probability that one or more cells in the victim row will flip and thus cause data corruption.
For example, during an activate command, a row in the volatile memory may be read and then written back to the volatile memory. During this process, electrons from one cell or row of cells may “leak” into a neighboring cell or row of cells, corrupting the neighboring data. This may be referred to as a “row hammer” error (also referred to as a “pass gate issue”). As another example, smaller memory cells may lose their charge more quickly than larger memory cells, and sometimes more quickly than a memory refresh interval. The result may be a loss and/or corruption of data. Other memory errors may be caused by cosmic rays and/or alpha particle emission. Many of these errors may be considered “soft” or “transient” because they may be readily correctable and not indicative of a more persistent underlying issue, such as hardware damage, malfunction, or defect.